Fix the check for an empty send socket buffer on a TOE TLS socket.

Compare sbavail() with the cached sb_off of already-sent data instead of
always comparing with zero.  This will correctly close the connection and
send the FIN if the socket buffer contains some previously-sent data but
no unsent data.

Reported by:	Harsh Jain @ Chelsio
Sponsored by:	Chelsio Communications

sys/dev/cxgbe/tom/t4_tls.c

@@ -1175,7 +1175,8 @@ t4_push_tls_records(struct adapter *sc, struct toepcb *toep, int drop)
 		 * Send a FIN if requested, but only if there's no
 		 * more data to send.
 		 */
-		if (sbavail(sb) == 0 && toep->flags & TPF_SEND_FIN) {
+		if (sbavail(sb) == tls_ofld->sb_off &&
+		    toep->flags & TPF_SEND_FIN) {
 			if (sowwakeup)
 				sowwakeup_locked(so);
 			else